Abstract:

An actuator system includes an actuator device comprising at least one
piezoelectric member, a driving system, and an actuator controller. The
driving system drives the at least one piezoelectric member at a driving
frequency. The actuator controller monitors at least one parameter of the
actuator device and the direct driving system to determine an operational
mechanical resonant frequency of the actuator device based on the at
least one parameter. The actuator controller adjusts the driving
frequency based at least in part on the determined operational mechanical
resonant frequency.

Claims:

1. An actuator system comprising:an actuator device comprising at least
one piezoelectric member;a driving system that drives the at least one
piezoelectric member at a driving frequency; andan actuator controller
that monitors at least one parameter of the actuator device and the
driving system to determine an operational mechanical resonant frequency
of the actuator device based on the at least one parameter, the actuator
controller adjusts the driving frequency based at least in part on the
determined operational mechanical resonant frequency.

2. The system as set forth in claim 1, wherein the actuator device further
comprises:an element with a threaded passage; anda threaded shaft with an
axis of rotation which extends through the threaded passage, the threaded
shaft at least partially engaged with at least a portion of the threaded
passage, the at least one piezoelectric member further comprises at least
two of the piezoelectric members operatively connected to the element.

3. The system as set forth in claim 2, wherein the driving system is
configured to provide the driving frequency which subjects the element to
vibrations causing the threaded shaft to simultaneously rotate and
translate in the direction along the axis of rotation through the element
and apply an axial force in the direction along the axis of rotation.

4. The system as set forth in claim 2, wherein the threaded shaft is
operatively connected to a load which is moveable in the direction along
the axis of rotation.

5. The system as set forth in claim 1, wherein the actuator device
comprises a structure with the at least one piezoelectric member and
having at least one point to frictionally couple to and drive a movable
element in at least one direction, the structure having at least two
bending modes, each of the bending modes having a different resonant
frequency, andwherein the driving system is configured to apply one or
more driving frequencies to each of the bending modes of the structure,
the driving frequency is substantially the same as one of the resonant
frequencies of the bending modes, wherein at the driving frequency, one
of the bending modes of the structure is vibrating substantially at
resonance and the other of the bending modes of the structure is
vibrating at partial resonance.

6. The system as set forth in claim 5, wherein the at least one parameter
is one of a current and a voltage of the driving frequency supplied to
the at least one piezoelectric member of the structure that vibrates
substantially at resonance.

7. The system as set forth in claim 5, wherein the driving frequency is
provided at a fixed offset from the resonant frequency of the bending
mode that is vibrating substantially at resonance.

8. The system as set forth in claim 1, wherein the driving system is a
direct driving system which provides a voltage boost for boosting an
input voltage.

9. The system as set forth in claim 1, wherein the driving system is a
resonant driving system comprising at least one tank circuit which
provides a voltage boost for boosting an input voltage.

10. The system as set forth in claim 9, wherein the at least one tank
circuit has an electrical resonant frequency which is substantially the
same as a nominal mechanical resonant frequency of the actuator device.

11. The system as set forth in claim 1, wherein the at least one parameter
is at least one electrical parameter of the actuator device and the
driving system.

12. The system as set forth in claim 11, wherein the at least one
electrical parameter comprises at least one of a current, a voltage, and
an impedance.

13. The system as set forth in claim 1, wherein the actuator controller
adjusts the driving frequency when the difference between the driving
frequency and the operational mechanical resonant frequency is at least
greater than an available frequency resolution step size.

14. The system as set forth in claim 13, wherein the available frequency
resolution step size is less than one percent of the operational
mechanical resonant frequency.

15. The system as set forth in claim 1 wherein the actuator controller
adjusts the driving frequency one or more times to identify at least one
of the operational mechanical resonant frequency and a set offset from
the operational mechanical resonant frequency.

16. The system as set forth in claim 15 wherein the driving system adjusts
the driving frequency within a set window about the operational
mechanical resonant frequency.

17. The system as set forth in claim 1, wherein the actuator controller
continuously monitors the at least one parameter through at least one
cycle of the actuator device.

18. The system as set forth in claim 1, wherein the driving system further
comprises at least one full bridge drive system.

19. The system as set forth in claim 1, wherein the driving system further
comprises at least one half bridge drive system.

20. The system as set forth in claim 1, wherein the actuator device
further comprises a first pair of opposing piezoelectric members
including a first piezoelectric member and a second piezoelectric member
and a second pair of opposing piezoelectric members including a third
piezoelectric member and a fourth piezoelectric member.

21. A method for making an actuator system, the method
comprising:providing an actuator device comprising at least one
piezoelectric member;operatively coupling a driving system to drive the
at least one piezoelectric member at a driving frequency; andoperatively
coupling an actuator controller to monitor at least one parameter of the
actuator device and the driving system to determine an operational
mechanical resonant frequency of the actuator device based on the at
least one monitored parameter, the actuator controller is configured to
adjust the driving frequency based at least in part on the determined
operational mechanical resonant frequency.

22. The method as set forth in claim 21, wherein the providing an actuator
device further comprises:providing an element with a threaded passage;
andat least partially engaging a threaded shaft with at least a portion
of the threaded passage, the at least one piezoelectric member further
comprises at least two of the piezoelectric members operatively connected
to the element.

23. The method as set forth in claim 22, wherein the operatively coupling
the driving system further comprises configuring the driving system to
provide the driving frequency which subjects the element to vibrations
causing the threaded shaft to simultaneously rotate and translate in the
direction along the axis of rotation through the element and apply an
axial force in the direction along the axis of rotation.

24. The method as set forth in claim 22, wherein the providing the
actuator device further comprises operatively connecting the threaded
shaft to a load which is moveable in the direction along the axis of
rotation.

25. The method as set forth in claim 21, wherein the providing the
actuator device further comprises providing a structure with the at least
one piezoelectric member and having at least one point to frictionally
couple to and drive a movable element in at least one direction, the
structure having at least two bending modes, each of the bending modes
having a different resonant frequency, andwherein the operatively
coupling the driving system further comprises configuring the driving
system to apply one or more driving frequencies to each of the bending
modes of the structure, the driving frequency is substantially the same
as one of the resonant frequencies of the bending modes, wherein at the
driving frequency, one of the bending modes of the structure is vibrating
substantially at resonance and the other of the bending modes of the
structure is vibrating at partial resonance.

26. The method as set forth in claim 25, wherein the at least one
parameter is one of a current and a voltage of the driving frequency
supplied to the at least one piezoelectric member of the structure that
vibrates substantially at resonance.

27. The method as set forth in claim 25, wherein the driving frequency is
provided at a fixed offset from the resonant frequency of the bending
mode that is vibrating substantially at resonance.

28. The method as set forth in claim 21, wherein the operatively coupling
the driving system further comprises operatively coupling a direct
driving system that provides a voltage boost for boosting an input
voltage.

29. The method as set forth in claim 21, wherein the operatively coupling
a driving system further comprises operatively coupling a resonant
driving system comprising at least one tank circuit which provides a
voltage boost for boosting an input voltage.

30. The method as set forth in claim 29, wherein the operatively coupling
a resonant driving system comprising the at least one tank circuit
further comprises providing the at least one tank circuit with an
electrical resonant frequency which is substantially the same as a
nominal mechanical resonant frequency of the actuator device.

31. The method as set forth in claim 21, wherein the at least one
parameter is at least one electrical parameter of the actuator device and
the driving system.

32. The method as set forth in claim 31, wherein the at least one
electrical parameter comprises at least one of a current, a voltage, and
an impedance.

33. The method as set forth in claim 21, wherein the operatively coupling
the actuator controller further comprises configuring the actuator
controller to adjust the driving frequency when the difference between
the driving frequency and the operational mechanical resonant frequency
is at least greater than an available frequency resolution step size.

34. The method as set forth in claim 33, wherein the available frequency
resolution step size is less than one percent of the operational
mechanical resonant frequency.

35. The method as set forth in claim 21 wherein the operatively coupling
the actuator controller further comprises configuring the actuator
controller to adjust the driving frequency one or more times to identify
at least one of the operational mechanical resonant frequency and a set
offset from the operational mechanical resonant frequency.

36. The method as set forth in claim 35 wherein the operatively coupling a
driving system further comprises configuring the driving system to adjust
the driving frequency within a set window about the operational
mechanical resonant frequency.

37. The method as set forth in claim 21, wherein the operatively coupling
the actuator controller further comprises configuring the actuator
controller to continuously monitors the at least one parameter through at
least one cycle of the actuator device.

38. The method as set forth in claim 21, wherein the operatively coupling
a driving system further comprises operatively coupling at least one full
bridge drive system to drive the at least one piezoelectric member at a
driving frequency.

39. The method as set forth in claim 21, wherein the operatively coupling
a driving system further comprises operatively coupling at least one half
bridge drive system to drive the at least one piezoelectric member at a
driving frequency.

40. The method as set forth in claim 21, wherein the actuator device
further comprises a first pair of opposing piezoelectric members
including a first piezoelectric member and a second piezoelectric member
and a second pair of opposing piezoelectric members including a third
piezoelectric member and a fourth piezoelectric member.

41. A method for controlling an actuator system, the method
comprising:monitoring with an actuator controller computing system at
least one parameter of an actuator device and a driving system coupled to
drive the actuator device at a driving frequency;determining with the
actuator controller computing system an operational mechanical resonant
frequency of the actuator device based on the at least one parameter;
andadjusting with the actuator controller computing system the driving
frequency provided by the driving system based at least in part on the
determined operational mechanical resonant frequency.

42. The method as set forth in claim 41 wherein the monitoring with the
actuator controller computing system further comprises continuously
monitors the at least one parameter through at least one cycle of the
actuator device.

43. The method as set forth in claim 41 wherein the at least one parameter
is one of a current and a voltage of the driving frequency provided to
the actuator device that vibrates substantially at resonance.

44. The method as set forth in claim 41 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency so one bending mode of the actuator device is vibrating
substantially at resonance and another bending mode of the actuator
device is vibrating at partial resonance.

45. The method as set forth in claim 41 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency to a fixed offset from the resonant frequency of a
bending mode of the actuator device.

46. The method as set forth in claim 41 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency when the difference between the driving frequency and
the operational mechanical resonant frequency is at least greater than an
available frequency resolution step size.

47. The method as set forth in claim 46 wherein the available frequency
resolution step size is less than one percent of the operational
mechanical resonant frequency.

48. The method as set forth in claim 41 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency one or more times to identify at least one of the
operational mechanical resonant frequency and a set offset from the
operational mechanical resonant frequency.

49. The method as set forth in claim 48 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency within a set window about the operational mechanical
resonant frequency.

50. A computer readable medium having stored thereon instructions for
controlling an actuator system comprising machine executable code which
when executed by at least one processor, causes the processor to perform
steps comprising:monitoring with an actuator controller computing system
at least one parameter of an actuator device and a driving system coupled
to drive the actuator device at a driving frequency;determining with the
actuator controller computing system an operational mechanical resonant
frequency of the actuator device based on the at least one parameter;
andadjusting with the actuator controller computing system the driving
frequency provided by the driving system based at least in part on the
determined operational mechanical resonant frequency.

51. The medium as set forth in claim 50 wherein the monitoring with the
actuator controller computing system further comprises continuously
monitors the at least one parameter through at least one cycle of the
actuator device.

52. The medium as set forth in claim 50 wherein the at least one parameter
is one of a current and a voltage of the driving frequency provided to
the actuator device that vibrates substantially at resonance.

53. The medium as set forth in claim 50 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency so one bending mode of the actuator device is vibrating
substantially at resonance and another bending mode of the actuator
device is vibrating at partial resonance.

54. The medium as set forth in claim 50 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency to a fixed offset from the resonant frequency of a
bending mode of the actuator device.

55. The medium as set forth in claim 50 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency when the difference between the driving frequency and
the operational mechanical resonant frequency is at least greater than an
available frequency resolution step size.

56. The medium as set forth in claim 55 wherein the available frequency
resolution step size is less than one percent of the operational
mechanical resonant frequency.

57. The medium as set forth in claim 50 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency one or more times to identify at least one of the
operational mechanical resonant frequency and a set offset from the
operational mechanical resonant frequency.

58. The medium as set forth in claim 57 wherein the adjusting with the
actuator controller computing system further comprises adjusting the
driving frequency within a set window about the operational mechanical
resonant frequency.

59. An actuator controller comprising:a monitoring system in an actuator
controller computing system that monitors at least one parameter of an
actuator device and a driving system coupled to drive the actuator device
at a driving frequency;a controller management system in the actuator
controller computing system that determines an operational mechanical
resonant frequency of the actuator device based on the at least one
parameter; andan adjustment system in the actuator controller computing
system that adjusts the driving frequency provided by the driving system
based at least in part on the determined operational mechanical resonant
frequency.

60. The system as set forth in claim 59 wherein the monitoring system in
the actuator controller computing system further monitors the at least
one parameter through at least one cycle of the actuator device.

61. The system as set forth in claim 59 wherein the at least one parameter
is one of a current and a voltage of the driving frequency provided to
the actuator device that vibrates substantially at resonance.

62. The system as set forth in claim 59 wherein the adjustment system in
the actuator controller computing system adjusts the driving frequency so
one bending mode of the actuator device is vibrating substantially at
resonance and another bending mode of the actuator device is vibrating at
partial resonance.

63. The system as set forth in claim 59 wherein the adjustment system in
the actuator controller computing system adjusts the driving frequency to
a fixed offset from the resonant frequency of a bending mode of the
actuator device.

64. The system as set forth in claim 59 wherein the adjustment system in
the actuator controller computing system adjusts the driving frequency
when the difference between the driving frequency and the operational
mechanical resonant frequency is at least greater than an available
frequency resolution step size.

65. The system as set forth in claim 64 wherein the available frequency
resolution step size is less than one percent of the operational
mechanical resonant frequency.

66. The system as set forth in claim 59 wherein the adjustment system in
the actuator controller computing system adjusts the driving frequency
one or more times to identify at least one of the operational mechanical
resonant frequency and a set offset from the operational mechanical
resonant frequency.

67. The system as set forth in claim 66 wherein the adjustment system in
the actuator controller computing system adjusts the driving frequency
within a set window about the operational mechanical resonant frequency.

[0003]Transducers using piezoelectric technologies are used for precise
positioning at the nanometer scale. Typically, piezoelectric devices
include a ceramic that is formed into a capacitor that changes shape when
charged and discharged. These piezoelectric devices can be used as
position actuators because of their shape changing properties (i.e.,
vibrations). When such a piezoelectric device is used as a position
actuator, the shape change of the ceramic is approximately proportional
to an applied voltage differential across the ceramic.

[0004]Several types of resonant motor systems and resonant actuator
systems use piezoelectric generated vibrations to create continuous
movement of elements with high speed, high torque, small size, and quiet
operation. An exemplary prior art motor is a linear motor system that
includes a threaded element or nut. The threaded element includes four
symmetrically positioned piezoelectric transducers or members. Driving
signals drive the transducers to simultaneous excite the orthogonal
bending modes of the threaded element at a first bending mode resonant
frequency. The driving signals are typically in the ultrasonic range with
a plus or minus ninety-degree phase shift to generate a circular orbit.
The threaded element orbits a threaded shaft at the first bending mode
resonant frequency, which generates torque that rotates the threaded
shaft that moves the threaded shaft linearly.

[0005]Examples of the above resonant motor systems and resonant actuator
systems may be found in U.S. Pat. No. 6,940,209, entitled, "Ultrasonic
Lead Screw Motor"; U.S. Pat. No. 7,339,306, entitled, "Mechanism
Comprised of Ultrasonic Lead Screw Motor"; U.S. Pat. No. 7,170,214,
entitled, "Mechanism Comprised of Ultrasonic Lead Screw Motor"; and U.S.
Pat. No. 7,309,943, entitled, "Mechanism Comprised of Ultrasonic Lead
Screw Motor," all of which are commonly assigned to New Scale
Technologies, Inc. and are all hereby incorporated herein by reference in
their entireties.

[0006]A controller typically generates and supplies one or more driving
signals to drive the piezoelectric transducers at a fixed driving
frequency. The fixed driving frequency is typically selected to be close
to a known or estimated nominal mechanical resonant frequency of the
actuator system. Driving the piezoelectric transducers at such a nominal
resonant frequency can increase the actuator's overall performance and
efficiency. Increases in performance can include faster rotational and
linear speeds and larger push forces. However, the resonant frequency of
these actuators change based on variables including, but not limited to,
ambient temperature, motor temperature, loading and manufacturing
tolerances. Thus, driving a motor system and/or an actuator system with a
fixed driving frequency can result in diminished performance over time.
This loss in performance can cause the actuator to be less efficient,
waste energy, run at slower than desired or optimal speeds, fail to move
a specific load, and add strain to the motor system and/or actuator
system.

[0007]Heretofore, some patents and publications have disclosed methods for
driving resonant actuator devices, which may be briefly summarized as
follows:

[0008]U.S. Pat. No. 5,233,274 to Honda et al. discloses a drive circuit
used in a Langevin type ultrasonic bolt-tightening motor in which a motor
drive voltage having a given frequency is applied to a piezo-electric
element in a stator section, the resulting longitudinal and torsional
vibrations being effective to rotate a motor section. The drive circuit
has a longitudinal vibration sensor for detecting the longitudinal
vibration in the stator section, a torsional vibration sensor for
detecting vibration in the stator section and a frequency controller for
controlling the frequency of the motor drive voltage such that the phase
difference between the detection signals of the longitudinal and
torsional vibration sensors becomes 90 degrees. The frequency of the
motor drive voltage can be feedback controlled to maintain an optimum
drive frequency despite the varying of the optimum drive frequency due to
changes in various factors. The disclosure of this patent is incorporated
herein by reference.

[0009]United States Patent Application Publication No. 2008/0129145 to Lee
et al. discloses a piezoelectric actuator for driving a piezoelectric
unit having two resonance points. The piezoelectric unit includes an
optimal driving frequency calculating unit that adds a delta frequency,
having a constant frequency difference from a first resonant frequency of
the piezoelectric unit, to a characteristic resonant frequency obtained
by analyzing characteristics of the piezoelectric unit, thereby
calculating an optimal driving frequency; and an FM modulating unit that
is connected to the optimal driving frequency calculating unit and
generates the optimal driving frequency, calculated by the optimal
driving frequency calculating unit, so as to supply to the piezoelectric
unit. The disclosure of this published patent application is incorporated
herein by reference.

[0010]United States Patent Application Publication No. 2009/0009109 to
Hashimoto discloses a method for driving an ultrasonic motor having an
actuator section. The method includes a step of starting the ultrasonic
motor by applying an AC voltage with a first frequency to the actuator
section; a voltage detection step of detecting a voltage generated at the
actuator section while lowering a driving frequency from the first
frequency to a second frequency at which the ultrasonic motor stops; a
starting step of starting the ultrasonic motor with a third frequency;
and a driving step of changing the driving frequency from the third
frequency to a lower frequency such that the driving frequency has a
value within an operation frequency range. The disclosure of this
published patent application is incorporated herein by reference.

SUMMARY

[0011]An actuator system in accordance with embodiments of the present
invention includes an actuator device comprising at least one
piezoelectric member, a driving system, and an actuator controller. The
driving system drives the at least one piezoelectric member at a driving
frequency. The actuator controller monitors at least one parameter of the
actuator device and the direct driving system to determine an operational
mechanical resonant frequency of the actuator device based on the at
least one parameter. The actuator controller adjusts the driving
frequency based at least in part on the determined operational mechanical
resonant frequency.

[0012]A method for making an actuator system in accordance with other
embodiments of the present invention includes providing an actuator
device comprising at least one piezoelectric member. A driving system is
operatively coupled to drive the at least one piezoelectric member at a
driving frequency. An actuator controller is operatively coupled to
monitor at least one parameter of the actuator device and the direct
driving system to determine an operational mechanical resonant frequency
of the actuator device based on the at least one monitored parameter. The
actuator controller is configured to adjust the driving frequency based
at least in part on the determined operational mechanical resonant
frequency.

[0013]A method for controlling an actuator system in accordance with
embodiments of the present invention includes monitoring with an actuator
controller computing system at least one parameter of an actuator device
and a driving system coupled to drive the actuator device at a driving
frequency. An operational mechanical resonant frequency of the actuator
device is determined with the actuator controller computing system based
on the at least one parameter. The driving frequency provided by the
driving system is adjusted with the actuator controller computing system
based at least in part on the determined operational mechanical resonant
frequency.

[0014]A computer readable medium in accordance with other embodiments of
the present invention includes having stored thereon instructions for
controlling an actuator system comprising machine executable code which
when executed by at least one processor, causes the processor to perform
steps including monitoring at least one parameter of an actuator device
and a driving system coupled to drive the actuator device at a driving
frequency. An operational mechanical resonant frequency of the actuator
device is determined based on the at least one parameter. The driving
frequency provided by the driving system is adjusted based at least in
part on the determined operational mechanical resonant frequency.

[0015]An actuator controller in accordance with other embodiments of the
present invention includes a monitoring system, a controller management
system, and an adjustment system in an actuator controller computing
system. The monitoring system monitors at least one parameter of an
actuator device and a driving system coupled to drive the actuator device
at a driving frequency. The controller management system determines an
operational mechanical resonant frequency of the actuator device based on
the at least one parameter. The adjustment system adjusts the driving
frequency provided by the driving system based at least in part on the
determined operational mechanical resonant frequency.

[0016]The present invention provides a number of advantages including
providing a higher performance and a more efficient motor system.
Additionally, the present invention provides better and more effective
control over resonant motor and actuator systems. Unlike prior systems,
the present invention does not require any external sensors, components
and/or circuits to determine motor or actuator performance to monitor and
control the driving frequency of a motor or actuator. Instead, the
present invention provides a drive frequency control for resonant
actuator systems which can automatically and continuously determine the
operational mechanical resonant frequency of the actuator by monitoring
at least one parameter of the actuator device and the direct driving
system. This control provided by the present invention adjusts the drive
frequency to match operational mechanical resonant frequency, regardless
of how the operational mechanical resonant frequency might vary due to
temperature fluctuations and/or variation of components within
manufacturing tolerances an without external sensors or devices. Further,
with the present invention the motor or actuator can directly operate on
about three volts while maximizing performance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1A is a perspective view of a direct drive actuator system in
accordance with embodiments of the present invention;

[0018]FIG. 1B is a cross-sectional side view of the direct drive actuator
system of FIG. 1A being driven by two driving signals;

[0019]FIG. 2 is a partial circuit and partial block diagram of the direct
drive actuator system illustrated in FIGS. 1A and 1B;

[0020]FIG. 3 is a graph of frequency versus current that illustrates a
change in peak current as temperature increases according to some
embodiments of the present invention;

[0021]FIG. 4A is a flow chart of an analog-to-digital converter interrupt
service method according to some embodiments of the present invention;

[0022]FIG. 4B is a flow chart of a timer interrupt service method
according to some embodiments of the present invention;

[0023]FIG. 4C is a flow chart of a frequency calibration method according
to some embodiments of the present invention;

[0024]FIG. 4D is a flow chart of a driver reload method according to some
embodiments of the present invention;

[0025]FIG. 5 is a partial circuit and partial block diagram of a resonant
drive actuator system in accordance with embodiments of the present
invention;

[0026]FIG. 6 is a graph of frequency versus current that illustrates a
change in minimum current as temperature increases according to some
embodiments of the present invention;

[0027]FIG. 7A is a flow chart of an analog-to-digital converter interrupt
service method according to some embodiments of the present invention;

[0028]FIG. 7B is a flow chart of a timer interrupt service method
according to some embodiments of the present invention;

[0029]FIG. 7C is a flow chart of a frequency calibration method according
to some embodiments of the present invention;

[0030]FIG. 7D is a flow chart of a driver reload method according to some
embodiments of the present invention;

[0031]FIG. 8A is partial perspective and partial circuit and block diagram
of a semi-resonant drive actuator system in accordance with embodiments
of the present invention; and

[0032]FIG. 8B is an end view of the actuator device illustrated in FIG. 8A
taken along line 8B-8B of FIG. 8A.

DETAILED DESCRIPTION

[0033]Motor systems and actuator systems have a nominal mechanical
resonant frequency, which is dependent on the system's physical
structure, materials, and temperature. Motor systems and actuator systems
can collectively be referred to as actuator systems or also as actuators.
The nominal mechanical resonant frequency of a particular batch of
actuator systems can vary from actuator to actuator based on
manufacturing mechanical tolerances. In some cases, manufacturing
mechanical tolerances can result in two actuators having mechanical
resonant frequencies that vary plus or minus two kilohertz. Additionally,
actuator temperature changes over time as the actuator heats up and/or as
the ambient temperature changes. These temperature changes also affect
the actuator's mechanical resonant frequency. As the nominal mechanical
resonant frequency of an actuator changes, the changing resonant
frequency is referred to as operational mechanical resonant frequency.

[0034]Three exemplary drive actuator systems 100(1)-100(3) in accordance
with embodiments of the present invention are illustrated and described
herein. More specifically, in these three examples the direct drive
actuator system 100(1) is illustrated and described with reference to
FIGS. 1A, 1B, and 2, the resonant drive actuator system 100(2) is
illustrated and described with reference to FIG. 5, and the semi-resonant
drive actuator system 100(3) is illustrated and described with reference
to FIGS. 8A and 8B. Each of these direct drive actuator systems
100(1)-100(3) mechanically excites the actuator device 102 or 802 in at
least a first bending mode. In these examples, the driving systems 230,
530, or 830 mechanically excite the first bending mode of the actuator
device 102 or 802 in two orthogonal planes in a cyclic manner. Put
another way, the driving systems 230, 530, or 830 cause the actuator
device 102 or 802 to bend in a Y-Z plane and in an X-Z plane.

[0035]The mechanical response of an actuator device 102 or 802 is greatest
when the driving system 230, 530, or 830 excites a bending mode of the
actuator device 102 or 802 with a driving signal having a driving
frequency equal to, or close to, the nominal mechanical resonant
frequency of the actuator. Thus, maximum performance of actuator systems
100(1)-100(3) is achieved with the greatest mechanical response. However,
because the nominal mechanical resonant frequency of the actuator can
change with e.g., temperature and manufacturing tolerances, the direct
driving systems and the resonant driving systems disclosed herein adjust
the driving frequency as the operational mechanical resonant frequency of
the actuator changes. Depending on the type and size of the actuator, the
driving frequency of the driving signal may for example be between about
fifty kilo-hertz and about one hundred eighty kilo-hertz. The following
disclosure describes systems and methods for monitoring changes to the
operational mechanical resonant frequency and making corresponding
changes or adjustments to the driving frequency to improve and/or
maximize the performance and efficiency of the actuator systems.

[0036]The direct driving systems and the resonant driving systems
disclosed herein can be used to drive a variety of actuators including,
but not limited to, linear motor systems, rotary motor systems,
semi-resonant actuator systems, and ultrasonic motor systems. It is to be
understood that any of the above mentioned variety of actuators can be
driven by both the direct driving systems and the resonant driving
systems disclosed herein, unless otherwise specified below.

[0037]The exemplary direct driving system 230, resonant driving system
530, and semi-resonant driving system 830 disclosed herein can be used to
maximize the performance and the efficiency of a variety of actuator
devices, such as exemplary actuator devices 102 and 802. For a given
input power the resonant driving system 530 yields higher actuator
performance than a direct driving system 230 operating at the same input
power. Thus, a first actuator device 102 driven by the resonant driving
system 530 operating at the same performance level (e.g., speed, push
force) as a second actuator device 102 driven by the direct driving
system 230 requires less input power. That is, in the above scenario, the
resonant driving system 530 is more efficient than the direct driving
system 230. A few non-limiting examples of actuator systems 100(1)-100(3)
with the direct driving system 230, the resonant driving system 530, or
the semi-resonant driving system 830 are discussed below, but it will
become apparent to those skilled in the art that aspects of the following
disclosure can be applied to any similar actuator or motor system with
other types of driving systems and actuator devices.

[0038]Referring more specifically to FIGS. 1A and 1B, the direct drive
actuator system 100(1) is illustrated in accordance with embodiments of
the present invention. The direct drive actuator system 100(1) includes
the actuator device 102 comprising an element 110 with a threaded
passage, a threaded shaft 120, and a direct driving system 230 (shown in
FIG. 2), although the direct drive actuator system 100(1) can include
other types and numbers of systems, devices, and components which are
connected in other manners. The present invention provides a controller
140 in the direct driving system 230 for maximizing the performance and
efficiency of the direct drive actuator system 100(1).

[0039]The actuator device 102 generates a force to move a load (e.g., an
optical lens) in a linear direction, although it is contemplated that the
actuator device 102 can move other types of loads in other directions.
The inner passage of the element 110 can be partially threaded or
threaded throughout. The threaded shaft 120 can be screwed into position
within the threaded passage of the element 110. The threaded shaft 120
has an axis of rotation 125 about which the threaded shaft 120 rotates.
The threaded shaft 120 also translates in a direction along the axis of
rotation 125. The threaded shaft 120 can include at least one rounded end
122 to reduce frictional forces and aid in applying the force to move the
load, although other types of ends can be used.

[0040]In addition to the element 110 and the threaded shaft 120, in this
example four piezoelectric members 132a-132d comprise part of the
actuator device 102, although the actuator device 102 can include other
types and numbers of systems, devices, and components and the
piezoelectric members can comprise part of the direct driving system
instead of the actuator device in other embodiments. Each piezoelectric
member 132a-132d is configured to change length upon being subjected to a
voltage differential across its thickness T. Specifically, the
piezoelectric members 132a-132d can expand and/or contract in the
direction along the axis of rotation 125 of the threaded shaft 120. Other
actuator devices that provide a force to move a load are contemplated,
including by way of example only an actuator device comprising two
piezoelectric members and an actuator device comprising a single
piezoelectric member.

[0041]Each of the piezoelectric members 132a-132d comprise a single layer
or plate of piezoelectric material. An electrode 133a-133d is coupled to
a top surface of one of the piezoelectric members 132a-132d,
respectively. The electrodes 133a-132d can be attached to the
piezoelectric members 132a-132d using various glues, adhesives, and/or
welding, although other manners for electrically coupling the electrodes
133a-133d to the piezoelectric members 132a-132d can be used. A bottom
surface of each of the piezoelectric members 132a-132d is rigidly
attached to a corresponding outer surface of the element 110. The
piezoelectric members 132a-132d can be attached to the element 110 using
various glues, adhesives, and/or welding, although other manners for
attaching the piezoelectric members 132a-132d can be used.

[0042]The flex circuit 134 also can be referred to as an electrical
coupler, although other types of electrical coupling systems can be used.
The flex circuit 134 electrically couples the electrodes 133a-133d
positioned on top of each piezoelectric member 132a-132d with the
controller 140 in driving system 230. The flex circuit 134 is configured
to be bent and/or wrapped around the element 110 such that conductive
terminals 136a-136d electrically couple to the piezoelectric members
132a-132d via the electrodes 133a-133d. The flex circuit 134 can be
predisposed to bend at certain locations to aid in wrapping the flex
circuit 134 around the piezoelectric members 132a-132d and the element
110. The flex circuit 134 comprises five conductive traces 135a-135e that
carry at least two different driving signals 144a-144b to the various
conductive terminals 136, although other amounts and numbers of
conductive traces and driving signals are contemplated, such as four
driving signals as illustrated and described with reference to FIGS. 8A
and 8B. For example, the flex circuit 134 can comprise four conductive
traces, wherein each conductive trace carries one of the driving signals.
The driving signals 144a-144b may also be referred to as electrical
signals, voltage signals, square-wave signals, or other types of input
signals.

[0043]The controller 140 has two signal outputs which in this example
provide square-wave driving signals 144a2-144b2 to the driver
assembly 260, although other types and numbers of signal outputs to other
systems, devices and assemblies can be used. Each of the two signal
outputs 144a2-144b2 are electrically coupled through the driver
assembly 260 to one of the conductive traces 135a-135d in the flex
circuit 134 to distribute one or more of the driving signals 144a-144b.
According to some embodiments, the fifth conductive trace 135e of the
flex circuit 134 is coupled to the element 110 and a bottom surface of
each of the piezoelectric members 132a-132d to ground. The grounding of
the bottom surfaces of the piezoelectric members 132a-132d allow the
direct driving system 230 to apply a voltage potential across the
thickness T of each piezoelectric member 132a-132d. The voltage potential
causes the piezoelectric members 132a-132d to expand and/or contract
thereby oscillating the element 110 and driving the threaded shaft 120 in
the direction along the axis of rotation 125.

[0044]Each of the conductive traces 135a-135e can be positioned such that
each conductive trace 135a-135e electrically attaches to a different
conductive terminal 136a-136e. The illustrated paths of the conductive
traces 135a-135e are by way of example only and not intended to limit the
actual layout of the paths of the conductive traces 135a-135e.

[0045]As shown in FIG. 1B, the driving signals 144a-144b are transmitted
to respective piezoelectric members 132a-132d. The first driving signal
144a is a square-wave voltage signal that is about 90 degrees out of
phase with respect to the second driving signal 144b, which is also a
square-wave voltage signal, although other types of signals with other
shapes and phase differentials can be used. In this particular example,
the first driving signal 144a is transmitted through conductive traces
135a and 135c that are attached via conductive terminals 136a and 136c to
the first piezoelectric member 132a and also to the third piezoelectric
member 132c. Additionally, in this particular example the second driving
signal 144b is transmitted through conductive traces 135b and 135d that
are attached via conductive terminals 136b and 136d to the second
piezoelectric member 132b and also to the fourth piezoelectric member
132d.

[0046]According to some embodiments, the first piezoelectric member 132a
and the third piezoelectric member 132c comprise a first pair of opposing
piezoelectric members 132a and 132c that operate together; and the second
piezoelectric member 132b and fourth piezoelectric member 132d comprise a
second pair of opposing piezoelectric members 132b and 132d that operate
together. The first driving signal 144a provided to the first pair of
opposing piezoelectric members 132a and 132c is phase shifted about 90
degrees relative to the second driving signal 144b provided to the second
pair of opposing piezoelectric members 132b and 132d to cause the
threaded shaft 120 to rotate and translate in the direction along the
axis of rotation 125. A positive 90 degree phase shift produces a
positive or forward translation of the threaded shaft 120 along the axis
of rotation 125, and a negative 90 degree phase shift produces a negative
or backward translation of the threaded shaft 120 along the axis of
rotation 125.

[0047]The actuator device 102 has a first bending direction and a second
bending direction, which is orthogonal to the first bending. Referring in
particular to FIG. 1A, the piezoelectric members 132a-132d are positioned
about the element 110 such that the first pair of opposed piezoelectric
members 132a and 132c bend the element 110 in a first pair of opposed
directions in Y-Z plane 101 as indicated by bidirectional arrow 103. In
like manner, the second pair of opposed piezoelectric members 132b and
132d bend the element 110 in a second pair of opposed directions in X-Z
plane 105 as indicated by bidirectional arrow 107. The first driving
signal 144a excites the first pair of piezoelectric members and the
second driving signal 144b excites the second pair of piezoelectric
members. The frequencies of the driving signals 144a-144b are
substantially the same as the nominal mechanical resonant frequency of
the element 110 of the actuator device 102. The excitation of the element
110 causes the cyclic orthogonal bending motion in the planes 101 and
105, which in turn causes the threaded shaft 120 to rotate and translate
in the direction along the axis of rotation 125. While certain driving
signals and phase shifts have been described, it is contemplated that
other frequency ranges, shapes, and phase differences of the driving
signals 144a-144b are contemplated. Specifically, the direct driving
system 230 can increase and/or decrease the driving frequency of the
driving signals to increase the performance and efficiency of the
actuator device 102. Additionally, while certain bending modes of the
actuator device 102 have been described, these bending modes are by way
of example only, the present invention is not limited to any number or
type of bending modes as each actuator and/or motor system can have other
types and numbers of bending modes.

[0048]Referring to FIG. 2, direct driving system 230 is shown operatively
coupled to the actuator device 102. As discussed above, the direct
driving system 230 can also be used to drive a variety of different
actuator devices including, but not limited to actuator device 102 and
also other linear motor systems employing multi-layer piezoelectric
plates as described in the aforementioned copending and commonly owned
U.S. patent application Publication Ser. No. 12/228,923; rotary motor
systems, semi-resonant actuator systems as described in the
aforementioned copending and commonly owned U.S. patent application
Publication Ser. No. 12/228,943; linear tube motor systems, rotary tube
motor systems, and ultrasonic motor systems. The direct driving system
230 can reside on a motherboard or computer chip. The direct driving
system 230 comprises a controller board or actuator controller system 250
and a driver assembly 260, although other numbers and types of boards or
chips can be used. The driver assembly 260 can also be referred to as an
actuator driver or a motor driver.

[0049]The actuator controller system 250 includes a processing system or
controller 140, a supply voltage or voltage source 253, a voltage boost
255, a current sensor 257, and a filter 259, although the actuator
controller system 250 can include other types and numbers of systems,
devices, and components which are connected in other manners. The
controller 140 can be a processor, a microprocessor, a microcontroller, a
digital signal processor or other controller motherboard, although other
numbers and types of controllers can be used The voltage source 253 is a
battery that supplies power to run, for example, the actuator device 102
and the various onboard electronics (e.g., controller 140), although
other types and numbers of power supplies can be used. In this example,
the voltage source 253 can supply a voltage of approximately 1.5 volts to
approximately 3.3 volts, although other ranges of voltages could be
supplied and used. The voltage boost 255 is coupled between the voltage
source 253 and the driver assembly 260. The voltage boost 255 increases
or boosts the supply voltage from the voltage source 253 to at least
about 25 volts, although the voltage boost 255 can increase the supply
voltage to approximately 40 volts or to other amounts for other
applications.

[0050]The current sensor 257 is coupled between the voltage source 253 and
the voltage boost 255 and monitors current usage of the driver assembly
260. The current sensor 257 detects an analog voltage drop across
resistor R which is proportional to the current drawn across the resistor
R by the driver assembly 260 for a fixed operating speed of the actuator
device 102 and the direct driving system 230. Thus, the voltage drop can
be used to calculate the current drawn by the actuator device 102 and the
direct driving system 230 using a multiplier.

[0051]The resistor R can have a resistance from about 0.025 ohms to about
1 ohms, although other ranges for the resistance and other types and
numbers of resistors in other combinations can be used, depending upon
the expected current usage. As the resistance of resistor R increases,
the voltage drop across the resistor R increases, which increases the
sensitivity of the current sensor 257. However, a larger voltage drop may
require a more powerful voltage source to maintain a sufficient power
supply to run the direct drive actuator system 100(1) and the onboard
electronics. The current sensor 257 also is coupled to the filter 259,
which removes the AC drive frequency component, although other
configurations can be used, such as having the current sensor 257
directly coupled to the controller 140 without a filter.

[0052]The controller 140 is directly coupled to the voltage source 253 and
to the filter 259, although the controller 140 could have other types and
numbers of connections. The controller 140 includes an analog-to-digital
converter 241 ("ADC") and a pulse width modulated ("PWM") signal
generator 242, although the controller 140 can include other types and
numbers of systems, devices, assemblies, and components in other
configurations, such as a master clock described later herein. The
analog-to-digital converter 241 receives the analog voltage signal as an
input from the filter 259 and converts that analog voltage signal into a
digital voltage value. The pulse width modulated signal generator 242 is
coupled to the driver assembly 260. The pulse width modulated signal
generator 242 generates at least two low-voltage driving signals
144a2 and 144b2 which are used to drive the piezoelectric
members 132a and 132c and the piezoelectric members 132b and 132d,
respectively, although the pulse width modulated signal generator 242
could generate other numbers and types of signals, such as four driving
signals which are out of phase with each other.

[0053]In this example, the controller 140 uses a multiplier, the value of
which is based on sensor resistor R and type of current sensor
electronics 257, to convert the digital voltage value into a digital
current value, which is used to determine a driving frequency of the two
low-voltage driving signals 144a2 and 144b2. The controller 140
can use the digital current value, a plurality of digital current values,
or an average digital current value to determine if an adjustment to the
drive frequency is getting closer or farther from the operational
mechanical resonant frequency of the actuator device 102. Put another
way, the controller 140 can cause the PWM signal generator 242 to adjust
a driving frequency of a generated signal (e.g., low-voltage driving
signals 144a2 and 144b2) up or down based at least in part on
digital current values.

[0054]The driver assembly 260 includes a first and a second half bridge
drive circuit 262a-262b, although the driver assembly 260 can include
other numbers and types of systems, devices, assemblies, and components
in other configurations. The first PWM driving signal 144a2 is
transmitted into the first half bridge drive circuit 262a. Power from the
voltage boost 255 feeds the first half bridge drive circuit 262a
according to the frequency and duty cycle of the PWM driving signal
144a2, which increases the amplitude or peak-to-peak voltage of the
first PWM driving signal 144a2. Similarly, the second PWM driving
signal 144b2 is transmitted into the second half bridge drive
circuit 262b. Power from the voltage boost 255 feeds the second half
bridge drive circuit 262b according to the frequency and duty cycle of
the PWM driving signal 144b2, which increases the amplitude or
peak-to-peak voltage of the second PWM driving signal 144b2.

[0055]Although half bridge drive circuits have been described, it is
contemplated that the first and second PWM driving signals 144a2 and
144b2 can be transmitted to respective first and second full bridge
drive circuits. One of the advantages of using full bridge drive circuits
is that the effective voltage differential across the positive electrode
and negative electrode of each of the piezoelectric members (e.g.,
piezoelectric members 132a-132d) is twice the supply voltage, which
effectively doubles the mechanical output as compared with a half bridge
circuit with the same supply voltage, which saves space. U.S. patent
application Ser. No. 12/228,923, entitled, "Reduced-Voltage, Linear Motor
Systems and Methods Thereof" provides additional description of the full
bridge drive circuit. Since the components and operation of half bridge
drive circuits and full bridge drive circuits are well known to those of
ordinary skill in the art, they will not be described in greater detail
herein.

[0056]The controller 140 can cause the PWM generator 242 to generate
driving signals of various frequencies, pulse widths and phase. For
example, the PWM generator 242 can generate a first signal having
frequency A, pulse width A, and phase A, and generate a second signal
having frequency A, pulse width A, and phase B. In some embodiments,
phase A is shifted about ninety degrees with respect to phase B, although
other amounts of phase shifting can be used. According to some
embodiments, the ninety degree phase shift between the first and second
driving signals 144a-144b causes the element 110 to orbit the threaded
shaft 120 at the mechanical resonant frequency of the element 110. The
orbiting of the element 110 generates torque that rotates the threaded
shaft 120 that moves the threaded shaft 120 linearly in the direction
along the axis of rotation 125.

[0057]Referring to FIG. 3, a chart of frequency versus current drawn 301
is shown that illustrates two general principles. Namely, when using
direct driving system 230 to drive an actuator device 102: (1) the
actuator device 102 and the direct driving system 230 draws maximum
current when the driving frequency of the driving signal is equal to or
close to the operational mechanical resonant frequency of the actuator
and (2) an increase in actuator temperature reduces the operational
mechanical resonant frequency of the actuator, thereby shifting the
maximum current peak.

[0058]The size and shape of an actuator device affects the actuator's
temperature coefficient, although other factors can affect the
temperature coefficient. Actuator devices having different temperature
coefficients can exhibit different frequency versus current relationships
than those shown in FIG. 3; however, the two general principles still
apply. For example, in an actuator device 102 operating at 1.8 volts
including an element having cross-sectional dimensions of about 1.8
mm×1.8 mm and a length of about six mm, the actuator device 102 has
a temperature coefficient of about negative forty hertz per degrees
Celsius (-40 Hz/° C.). Thus, the operational resonant frequency of
the actuator device 102 decreases about 40 Hertz for every one degree
Celsius increase in temperature. Various other types and sizes of
actuator devices having various temperature coefficients are contemplated
as exhibiting the same two general principles. Accordingly, FIG. 3 serves
as an example that illustrates how changes in the temperature and/or
ambient temperature of an actuator device can affect an operational
mechanical resonant frequency of the actuator device over time.

[0059]Referring more specifically to FIG. 3, three different plots taken
at three different times of the example above of the actuator device 102
driven by the direct driving system 230 are illustrated. Temp 1
illustrates that the maximum current drawn on startup of the motor is
about 103 milliamps at a driving frequency fRo, which is about 172.5
Kilohertz. Temp 2 illustrates that the maximum current drawn after
warming up the motor is about 103 milliamps at a driving frequency
fR2, which is about 171 kilohertz. Temp 3 illustrates that the
maximum current drawn at steady state operation of the motor increased to
about 112 milliamps at a driving frequency fR3, which is about 171
kilohertz. Thus, over time as the actuator device 102 in this example
heats up, the operational mechanical resonant frequency of the actuator
device 102 decreases and the current drawn by the actuator device 102 and
the direct driving system 230 also decreases unless the driving frequency
is tracking the mechanical resonant frequency.

[0060]To maximize performance and efficiency of the actuator device 102
driven by the direct driving system 230, the controller 140 in the direct
driving system 230 monitors the current drawn by the actuator device 102
and the direct driving system 230 and compares the current drawn over
time with average usages of previously drawn current. Based on the
comparison of current usages, the controller 140 can estimate the
operational mechanical frequency of the actuator device 102. Depending on
whether the operational mechanical resonant frequency is less than,
greater than, or about the same as the nominal or previously determined
operational mechanical resonant frequency, the controller 140 adjusts the
driving frequency of the two low-voltage driving signals 144a2 and
144b2, although the controller 140 can modify other aspects of the
same or different signals. For the exemplary actuator device 102
described earlier for which the data of FIG. 3 is provided, the
adjustment range of the direct driving system 230 is between about 166
kilohertz and about 176 kilohertz. In general, for any given actuator
device, the adjustment range of the direct driving system will be within
±3 percent of the operational mechanical resonant frequency of the
actuator device. Depending upon the design of the resonant actuator
device, the operational mechanical resonant frequency may vary widely,
such as between about 20 kilohertz and about one megahertz by way of
example.

[0061]The controller 140 monitors the current usage of the actuator device
102 and the direct driving system 230 and maximizes motor performance and
efficiency by adjusting and/or stepping the driving frequency to be
closer to the frequency that results in maximum current usage. Put
another way, when using a direct driving system 230, performance and
efficiency of the actuator device 102 are maximized when the actuator
device 102 is driven with driving signals 144a-144b at a driving
frequency as close as possible to the operational mechanical resonant
frequency of the actuator device 102. The drive frequency step size
determines how close the drive frequency can get to the operational
mechanical resonant frequency. Drive frequencies can be created by
dividing a fixed master clock or oscillator. The higher the master clock
frequency, the smaller the drive frequency step and the closer the drive
frequency may get to the operational mechanical resonant frequency. Drive
frequencies also can be created by direct control of a voltage controlled
oscillator or VCO, tuned to the operational frequency range of the
actuator, or a combination of a high frequency VCO and division.

[0062]The controller 140 described earlier also includes a master clock
with a maximum clock frequency. The master clock frequency can range from
at least about nine megahertz to at least about forty megahertz, although
other clock frequencies can be used, such as a clock frequency of at
least about 20 megahertz. The adjustments by the controller 140 to the
driving frequency are limited by an available frequency resolution, or an
available frequency resolution step size. For example, a controller 140
implementing a twenty megahertz master clock that generates driving
signals with a driving frequency of about 171 kilohertz has an available
driving frequency resolution of about 1.4 kilohertz. In this example, the
controller 140 can adjust the driving frequency to at least be within 700
hertz of the operational mechanical resonant frequency. The available
frequency resolution step size of a controller 140 varies with master
clock frequency and driving frequency. It is contemplated that various
master clock frequencies and various driving frequencies can be
implemented to yield many different frequency resolution step sizes. For
example, a controller 140 with a master clock frequency of about forty
megahertz generating a driving signal at a driving frequency of about 171
kilohertz has an available frequency resolution step size of about seven
hundred hertz, although other embodiments can have other frequency
resolution step sizes, such as at least about fifty hertz or at least
about three hundred hertz by way of example only.

[0063]The master clock frequency selection is a compromise between cost,
power consumption (since power usage goes up with frequency), and
achieving a drive frequency step size that provides a minimum level of
performance from the actuator regardless the operational mechanical
resonant frequency. The particular frequency resolution can vary based on
the particular application. By way of example only, a frequency
resolution of no more than about 1.4 kilohertz is sufficient to provide
the minimum performance required for a 1.8 motor across the operational
temperature range.

[0064]In some embodiments where the available master clock frequency is
too low to achieve minimal performance requirements because the resulting
drive frequency steps size is to large and therefore unable to remain
close to the operational mechanical resonant frequency, a phase locked
loop or PLL may be used to multiply the master clock. One particular
embodiment uses clock a doubler which may be implemented for master clock
frequencies at or below 10 megahertz.

[0065]Referring to FIGS. 4A-4D, four flow diagrams are shown that
illustrate the operation of software and/or firmware in or on the
actuator controller system 250 and/or the driver assembly 260. Referring
more specifically to FIG. 4A, an exemplary ADC interrupt service method
(ISM) 470 is illustrated and described. As discussed above in relation to
FIG. 2, the current sensor 257 monitors current usage of the driver
assembly 260. The voltage across the current sensor 257 is proportional
to the current drawn across the resistor R. In step 471, the ADC 241
periodically receives an analog voltage signal generated by the current
sensor 257 and converts that analog voltage into a digital voltage value,
also known as an ADC digital voltage value. Once a new digital voltage
value is obtained, in step 472 the oldest stored digital voltage value is
subtracted from a running total stored in random access memory on the
actuator controller system 250. In step 473, the oldest subtracted
digital voltage value is then replaced with the new received digital
voltage value and added into the running total. Next in step 474, the ADC
241 then awaits its next sample acquisition which depends on a
predetermined acquisition time increment.

[0066]The running total of digital voltage values includes at least about
thirty digital voltage values, although other numbers of digital voltage
values can be used, for example, one, ten or twenty. The running total of
digital voltage values can be averaged by dividing the running total by
the number of samples. The averaging of samples can be used to reduce the
effects of noise in the direct driving system 230 and/or in the actuator
device 102. The controller 140 obtains a new digital voltage value at
least about every twenty microseconds, although the controller 140 can
obtain a value more or less frequently, for example, every five
microseconds or every one hundred microseconds.

[0067]Referring more specifically to FIG. 4B, an exemplary timer interrupt
service method (ISM) 476 is illustrated and described. The actuator
controller system 250 discussed above and shown in FIG. 2, has a pulse
count register that is reloaded periodically to generate a continuous
drive signal. In some embodiments, elements of the actuator controller
system 250, such as the PWM generator, are combined with the driver
assembly 260 and contain the pulse counter therein. In step 477, the
controller 140 begins to perform frequency calibration, if enabled, and
reload the pulse count register. In step 478, the controller 140 converts
the running total of digital voltage values (e.g., thirty digital voltage
values) into a running total of digital current values. The running total
of digital current values can be averaged by dividing by the total number
of samples (e.g., thirty samples). This average digital current value is
about equal to the average current drawn by the driver assembly 260 and
actuator device 102 over a predetermined period of time (e.g., twenty
microseconds×thirty samples=600 microseconds).

[0068]After the running total of digital voltage values is converted into
current values, in step 479 the controller 140 determines if frequency
calibration is enabled. A user or the controller 140 can turn frequency
calibration on or off. In some embodiments, the user turns frequency
calibration off to manually adjust the driving frequency. Other reasons
for turning frequency calibration are contemplated, such as when ramping
the speed of the motor as this affects the current apart from the drive
frequency. If in step 479 controller 140 determines the frequency
calibration is not enabled, then the No branch is taken to step 481 where
the controller 140 immediately reloads a buffer with the previously
stored driving frequency and pulse count.

[0069]If in step 479 controller 140 determines the frequency calibration
is enabled, then the Yes branch is taken to step 480 where the controller
140 determines if the driving frequency is being held, that is awaiting
the next calibration time interval. The direct driving system 230 can
hold the driving frequency constant for a period of time. In some
instances, constantly changing and/or adjusting the driving frequency can
reduce actuator performance and actuator efficiency. For example, once
the direct driving system 230 finds the operational mechanical resonant
frequency of the actuator device 102, the controller 140 adjusts the
driving frequency and can put a hold on the new driving frequency. The
hold can be for a predetermined amount of time, for example, thirty
seconds, or the hold can be until the controller 140 detects a
predetermined increase or decrease in current usage by the driving
circuit 260. If in step 480 the controller 140 determines the driving
frequency is not being held, then the No branch is taken to step 483
where the controller 140 calibrates the driving frequency as illustrated
and described herein with reference to FIG. 4C.

[0070]If in step 480 the controller 140 determines the driving frequency
is being held, then the Yes Branch is taken to step 482 where the
controller 140 determines if there is a significant drop in current
usage. A significant drop of current usage can indicate that the actuator
device 102 is not operating at peak performance and maximum efficiency
because the operational mechanical resonant frequency of the actuator
device 102 changed. If in step 480 the controller 140 determines there is
no significant drop in current usage, then the No branch is taken to step
481 where the controller 140 immediately reloads a buffer with the
previously stored driving frequency and pulse count. If in step 480 the
controller 140 determines there is a significant drop in current usage,
then the Yes branch is taken to step 484. In step 484, even though there
is a hold on the frequency, the controller 140 lowers the driving
frequency and restarts calibration. The controller 140 default state
lowers the driving frequency because a significant drop in current
typically indicates a reduction of the operational mechanical resonant
frequency of the actuator device 102. A significant drop in current can
be at least about five milliamps, but this can vary between motor types.
Next following the lowering of the driving frequency and the restarting
of calibration in step 484, in step 481 the controller 140 immediately
reloads a buffer with the previously stored driving frequency and pulse
count.

[0071]Referring back to FIG. 3, as the motor warmed up, the operational
mechanical resonant frequency decreased from about 172.5 kilohertz to
about 171 kilohertz. Comparing the Temp 1 plot to the Temp 2 plot
illustrates this point. Initially, the maximum current usage was at
fR0, which is at about 172.5 kilohertz. Later on in time, the
maximum current usage was at fR2, which is at about 171 kilohertz.
The maximum current usage initially was at about 103 milliamps. Continual
monitoring of current usage of the driver board, while keeping the
driving frequency at about 172.5 kilohertz indicates that the maximum
current would drop to about 91 milliamps. Further comparison with the
Temp 3 plot indicates that maintaining the driving frequency at about
172.5 kilohertz results in the maximum current usage dropping to about 84
milliamps. Each of these drops in current usage indicates that the
operational mechanical resonant frequency changed. Changes of operational
mechanical resonant frequency in typical actuator device initially are
the result of increases in temperature due to the actuator device warming
up. As the temperature of the actuator device rises, the operational
mechanical resonant frequency decreases. Thus, default of the timer ISM
476 executed by the controller 140 is in step 484 to lower the driving
frequency after detecting in step 482 a significant drop of current.
After lowering the driving frequency and restarting calibration in step
484, the controller 140 loads the buffer with the new driving frequency
and pulse count in step 481.

[0072]Referring to FIG. 4C, a flow chart is shown that illustrates in
greater detail the driving frequency calibration method of step 483.
Referring also to FIG. 4B, if in step 479 frequency calibration is
enabled and the driving frequency is not held in step 480, then in step
483 the controller 140 will calibrate the driving frequency. Initially,
in step 487 the controller 140 checks an ADC current sample count. If in
step 487 the controller 140 determines the current sample count is less
than one, then the Yes branch is taken to step 481 where the controller
140 reloads the buffer with the previously stored driving frequency and
pulse count because the controller 140 needs at least two current samples
for comparison. The current sample is the average digital current value
discussed above in relation to FIG. 4B. It is contemplated that instead
of analyzing and/or comparing electrical current values to determine
changes in the operational mechanical resonant frequency, the controller
140 can analyze and/or compare other types of values, such as
peak-to-peak voltage values, power values, impedance values, or any
combination thereof.

[0073]If in step 487 the controller 140 determines the ADC current sample
count is not less than one, then the No branch is taken to step 488 where
the controller 140 determines if the ADC current sample count is equal to
one. If in step 488, the controller 140 determines the ADC current sample
count is equal to one, then the Yes branch is taken to step 489 and a
step direction and a direction change count are cleared. The change
direction count tracks the number of times the controller 140 changes the
step direction. The step direction determines whether the driving
frequency will be increased or decreased. For example, referring to FIG.
3, if the step direction is downward, the initial driving frequency
fRo will be reduced from 172.5 kilohertz by the frequency resolution
step size of the controller 140, which results in a lower driving
frequency (e.g., 171.1 kilohertz). Similarly, if the step direction is
upward, the driving frequency will be increased from 172.5 kilohertz by
the frequency resolution step size of the controller 140, which results
in a higher driving frequency (e.g., 173.9 kilohertz).

[0074]An ADC current sample count equal to one typically means that the
actuator device 102 was just turned on and that the step direction and
direction change count, which affect the frequency calibration in step
483, should be initialized. Initializing the direction change count sets
the counter to zero. Initializing the step direction in step 489 sets the
step direction downward, which incrementally decreases the driving
frequency by the frequency resolution of the controller 140, although
initializing the step direction can change the step direction to upward
in other embodiments. The step direction in step 489 initially is set
downward because operational temperature of most actuator devices
increase due to the actuator device warming up, which decreases the
operational resonant frequency of the actuator device, although the step
direction could be set upward in other embodiments. Once the driving
frequency is lowered, then in step 481 the controller 140 reloads the
buffer with the new driving frequency and pulse count. According to other
embodiments, initializing the step direction sets the step direction
upward, which incrementally increases the driving frequency by the
frequency resolution step size of the controller 140.

[0075]If in step 488 the controller 140 determines the ADC current sample
count is not equal to one, that indicates there are at least two ADC
current samples available for comparison and the No branch is taken to
step 490. One of the at least two current samples is a maximum recorded
current sample. In step 490, the controller 140 calculates the difference
between the latest current sample with the maximum recorded current
sample in the same step direction (e.g., down).

[0076]In step 491, the controller 140 determines if the latest current
sample has decreased. If in step 491 the controller 140 determines the
latest current sample has decreased, then the Yes branch is taken to step
492 where the step direction is changed and the direction change counter
is incremented. For example, if the initial step direction is downward,
then in step 492 the controller 140 will change the direction to upward.
If in step 491 the controller 140 determines the latest current sample
has remained constant or increased, then the No branch is taken to step
493 where the driving frequency is stepped by the frequency resolution of
the controller 140 according to the previously stored step direction
(e.g., downward). After the driving frequency is stepped according to the
last direction in step 493, then the controller 140 reloads the buffer
with the new driving frequency and pulse count in step 481.

[0077]If in step 491 the controller 140 determines the latest current
sample has gone down, then after the step direction is inverted and the
direction change count is incremented in step 492), the controller 140
determines in step 494 if the direction change count is greater than two.
If in step 494 the controller 140 determines the direction change count
is greater than two, then yes branch is taken to step 495 where the
controller 140 resets the driving frequency to the driving frequency that
produced the latest recorded maximum current sample and the direct
driving system 230 is switched to the hold driving frequency mode. After
the driving frequency is reset by the controller 140 in step 495, the
controller 140 reloads the buffer with the new driving frequency and
pulse count in step 481. If in step 494 the controller 140 determines the
direction change count is less than or equal to two, then the No branch
is taken to step 496 where driving frequency is stepped by the frequency
resolution of the controller 140 according to the new step direction
(e.g., upward). After the driving frequency is stepped according to the
new step direction in step 496, then the controller 140 reloads the
buffer with the new driving frequency and pulse count in step 481.

[0078]Referring to FIG. 4D, a flow diagram of the driver reload method of
step 481 is shown according to some embodiments. Several scenarios in the
timer ISM 476 and the frequency calibration method of step 483 end with
the driver reload method of step 481. The driver reload method of step
481 loads the buffer with the frequency of the driving signal and/or
period if the frequency changed. The driver reload method of step 481
also reloads the pulse count such that the controller 140 can
continuously generate a driving signal (e.g., driving signals 144a-144b).
After the buffer is reloaded, the controller 140 continues to run the ADC
ISM 470 and the timer ISM 476 periodically to monitor the current and
determine whether to further adjust the driving frequency of the driving
signals (e.g., driving signals 144a-144b). The controller 140 runs the
frequency calibration method of step 483 about every eight hundred
microseconds, although the frequency calibration method of step 483 can
be run more or less frequently, for example, every four hundred
microseconds or every sixteen hundred microseconds.

[0079]Now referring to FIG. 5, a resonant drive actuator system 100(2)
with a resonant driving system 530 operatively coupled to the actuator
device 102 which was illustrated and described earlier. As discussed
above, the resonant driving system 530 can be used to increase
performance and maximize efficiency of the variety of actuator devices
including, but not limited to actuator device 102, such as motor systems
employing single or other numbers of piezoelectric plates, rotary motor
systems, semi-resonant actuator systems, linear tube motor systems,
rotary tube motor systems, and ultrasonic motor systems. The resonant
driving system 530 uses a driving system that is the same as the direct
driving system 230 discussed above in relationship to FIGS. 1A-1B and 2,
except as described and illustrated herein. The resonant driving system
530 resides on a circuit board such as a "motherboard," or on a computer
chip such as an application specific integrated circuit (ASIC), although
other formats for the driving system can be used. The resonant driving
system 530 comprises a controller circuit or actuator controller 550 and
a driver assembly 560 provided on one or more integrated circuit chips
and/or one or more circuit boards, although other numbers and types of
boards or chips can be used. The actuator controller 550 and the driver
assembly 560 may be contained on a single ASIC chip. The driver assembly
560 can also be referred to as an actuator driver or a motor driver by
way of example only.

[0080]The actuator controller 550 includes a controller 540, a supply
voltage or voltage source 553, a current sensor 557, and a filter 559,
although the actuator controller 550 can include other numbers and types
of systems, devices, and components, which are connected in other
manners. The actuator controller 540 can be a processor, a
microprocessor, a microcontroller, a digital signal processor, and/or a
motherboard, although other types and numbers of controllers can be used.
The voltage source 553 may be provided as a part of the actuator
controller 550 and coupled to the controller 540, the current sensor 557,
and the driver assembly 560, although the voltage source 553 can be
coupled with any number of additional or fewer components. The voltage
source 553 is the same as the voltage source 253 described above in
relation to FIG. 2.

[0081]The current sensor 557 may be provided as a part of the actuator
controller 550 and coupled between the voltage source 553 and the driver
assembly 560, such that the current sensor 557 monitors current usage of
the driver assembly 560. The current sensor 557 is the same as the
current sensor 257 described above in relation to FIG. 2. The current
sensor 557 detects an analog voltage drop across resistor R, also called
an analog voltage signal. The voltage drop across the current sensor 557
is proportional to the current drawn across the resistor R by the driver
assembly 560 for a fixed operating speed of the actuator device 102.
Thus, the voltage drop can be used to calculate the current drawn by the
actuator device 102 and the resonant driving system 530 using a
multiplier.

[0082]The resistor R can have a resistance from about 0.025 ohms to about
1 ohms, although other ranges for the resistance and other types and
numbers of resistors in other combinations can be used depending on the
expected current usage. As the resistance of resistor R increases, the
voltage drop across the resistor R increases, which increases the
sensitivity of the current sensor 557. However, a larger voltage drop may
require a higher voltage source to maintain a sufficient power supply to
run the actuator device 102 and the onboard electronics. The current
sensor 557 also is coupled to the filter 559, which removes the AC drive
frequency component, although other configurations can be used, such as
having the current sensor 557 be directly coupled to the controller 540
without a filter.

[0083]The controller 540 is directly coupled to the voltage source 553,
the filter 559, and the driver assembly 560, although the controller can
be coupled to other types and numbers of systems, devices, assemblies,
and components in other configurations. The controller 540 includes an
analog-to-digital converter 541 ("ADC") and a pulse width modulated
("PWM") signal generator 542, although the controller 540 can include
other types and numbers of systems, devices, assemblies, and components
in other configurations, such as a master clock described later herein.
The controller 540 includes an analog-to-digital converter 541 ("ADC")
that receives the analog voltage signal as an input from the filter 559
and converts that analog voltage signal into a digital voltage value. The
controller 540 also includes a pulse width modulated ("PWM") signal
generator 542 that is coupled to the driver board 560. The PWM signal
generator 542 generates at least two low-voltage driving signals
544a2 and 544b2 which are used to drive the piezoelectric
members 132a and 132c and the piezoelectric members 132b and 132d,
respectively.

[0084]The controller 540 uses a multiplier, the value of which is based on
sensor resistor R and type of current sensor electronics 557 to convert
the digital voltage value into a digital current value, which is used to
determine a driving frequency of the two low-voltage driving signals
544a2-544b2. The controller 540 can use by way of example the
digital current value, a plurality of digital current values, or an
average digital current value to determine if an adjustment to the drive
frequency is getting closer or further from the operational mechanical
resonant frequency of the actuator device 102. Put another way, the
controller 540 can cause the PWM signal generator 542 to adjust a driving
frequency of a generated signal (e.g., low-voltage driving signals
544a2-544b2) up or down based at least in part on digital
current values.

[0085]The driver assembly 560 includes a first and a second half bridge
drive circuit 562a-562b and a first and second tank circuit 564a-564b,
although the driver assembly 560 can include other numbers and types of
circuits and components connected in other manners, such as full bridge
drive circuits and/or four half bridge drive circuits. The first PWM
driving signal 544a2 is transmitted into the first half bridge drive
circuit 562a on the driver board 560. Power from the voltage source 553
feeds the first tank circuit 564a according to the frequency and duty
cycle of the low voltage driving signal 544a2, which results in the
first driving signal 544a. Similarly, the second PWM driving signal
544b2 is transmitted into the second half bridge drive circuit 562b
on the driver assembly 560. Power from the voltage source 553 feeds the
second tank circuit 564b according to the frequency and duty cycle of the
low voltage driving signal 544b2, which results in the second
driving signal 544b.

[0086]The first and second tank circuits 564a-564b are also referred to as
LC circuits or inductor-capacitor circuits. According to some
embodiments, the tank circuits 564a-564b have an electrical resonant
frequency close to the nominal mechanical resonant frequency of the
actuator device 102. Tank circuits having an electrical resonant
frequency within one thousand hertz of the nominal mechanical resonant
frequency of the actuator device 102 are contemplated, although other
types of circuits with other parameters can be used. The tank circuits
564a-564b can be used to boost the peak-to-peak voltage of the first and
second driving signals 544a-544b. The tank circuits 564a-564b recycle
energy stored in the bulk capacitance of the actuator device 102. The
bulk capacitance of the actuator device 102 includes the capacitance of
capacitor C and the capacitance of the piezoelectric members 132a-132d.
Recycling the bulk capacitance of the actuator device 102 increases the
efficiency of the actuator device 102. Additionally, recycling of the
energy produces the first and second driving signals 544a-544b having
peak-to-peak voltages of at least about fifty volts depending upon the
electrical Q of the circuit, although the recycling of the energy can
produce driving signals having greater or lower peak-to-peak voltages,
such as, for example, at least about one hundred volts and/or at least
about two hundred volts.

[0087]Referring to FIG. 6, a graph 601 of frequency versus current drawn
is shown that illustrates two general principles. Namely, when using
resonant driving system 530 to drive an actuator device 102: (1) the
actuator device 102 and resonant driving system 102 draws minimum current
when the driving frequency of the driving signal is equal to, or close
to, the operational mechanical resonant frequency of the actuator device
102 and (2) an increase in temperature of the actuator device 102 reduces
the operational mechanical resonant frequency of the actuator device 102,
thereby shifting the minimum current peak.

[0088]According to some embodiments, the size and shape of an actuator
device affects the temperature coefficient of the actuator device.
Actuator devices having different temperature coefficients can exhibit
different frequency versus current relationships than those shown in FIG.
6; however, the two general principles still apply. For example, in an
actuator device 102 including an element 110 having cross-sectional
dimensions of about 3.4 mm×3.4 mm and a length of about 10 mm
(i.e., a 3.4 linear motor), the actuator device 102 has a temperature
coefficient of about negative twenty-seven hertz per degrees Celsius (-27
Hz/° C). Thus, the operational resonant frequency of the actuator
device 102 decreases about 27 hertz for every one degree Celsius increase
in temperature. Various other types and sizes of actuator devices having
various temperature coefficients are contemplated as exhibiting the same
two general principles. Thus, FIG. 6 should not be limited to a specific
actuator device, but rather to serve as an example that illustrates how
changes in temperature and/or ambient temperature of the actuator device
can affect an operational mechanical resonant frequency of the actuator
device over time.

[0089]Referring more specifically to FIG. 6, three different plots taken
at three different times of actuator device 102 driven by a resonant
driving system 530 are illustrated. Temp 1 illustrates that the minimum
current drawn on startup of the actuator device 102 is about 19 milliamps
at a driving frequency fRo, which is about 170.7 Kilohertz. Temp 2
illustrates that the minimum current drawn after warming up the actuator
device 102 is about 19 milliamps at a driving frequency fR2, which
is about 170.4 kilohertz. Temp 3 illustrates that the minimum current
drawn at steady state of the actuator device 102 is about 19 milliamps at
a driving frequency fR3, which is about 170.0 kilohertz. Thus, over
time as the actuator device 102 heats up, the operational mechanical
resonant frequency of the actuator device 102 decreases and the current
drawn increases unless the driving frequency is tracking the mechanical
resonant frequency.

[0090]To maximize efficiency and to increase performance of the actuator
device 102 driven by the resonant driving system 530, the controller 540
monitors the current drawn and compares the current drawn over time with
average usages of previously drawn current. Based on the comparison of
current usages, the controller 540 can estimate the operational
mechanical frequency of the actuator device 102. Depending on whether the
operational mechanical resonant frequency is less than, greater than, or
about the same as the nominal or previously determined operational
mechanical resonant frequency, the controller 540 adjusts and/or steps
the driving frequency of the two low-voltage driving signals 544a2
and 544b2, although the controller 140 can modify other aspects of
the same or different signals. For the exemplary actuator device 102
operating at 3.4 volts for which the data of FIG. 6 is provided, the
adjustment range of the resonant driving system 530 is between about 166
kilohertz and about 176 kilohertz, although other ranges can be used. In
general, for any given actuator system, the adjustment range of the
resonant driving system will be within ±3 percent of the operational
mechanical resonant frequency of the actuator device 102, although other
percentages can be used.

[0091]The controller 540 monitors the current usage of the actuator device
102 and the resonant driving system 530 and adjusts and/or steps the
driving frequency to be closer to the frequency that results in minimum
current and/or voltage usage. Such adjustments to the driving frequency
result in near maximum performance and maximum efficiency of the actuator
device 102. Put another way, when using a resonant driving system 530,
efficiency of the actuator device 102 is maximized and performance is
increased when the actuator device 102 is driven with driving signals
544a-544b at a driving frequency as close as possible to the operational
mechanical resonant frequency of the actuator device 102.

[0092]The controller 540 includes a master clock with a maximum clock
frequency. The master clock is the same as, or similar to, the master
clock discussed above in relation to FIG. 2. As discussed above in
relation to the direct driving system 230 in FIG. 2, the master clock
frequency ranges from at least about nine megahertz to at least about
forty megahertz. Other clock frequencies are contemplated such as a clock
frequency of at least about 20 megahertz.

[0093]The proximity of the driving frequency of the driving signals
544a-544b to the operational mechanical resonant frequency of the
actuator device 102 depends on the available master clock frequency,
which in turn limits an available frequency resolution step size as
described above. According to some embodiments, the controller 540
includes a master clock that feeds a direct digital synthesis (DDS) chip.
The DDS chip can modulate between adjacent frequencies to provide a
greater frequency resolution. For example, a controller 540 implementing
the DDS chip can adjust the driving frequency in incremental steps of at
least about fifty hertz, although the controller 540 and the DDS chip can
have other frequency resolutions such as, for example about three hundred
hertz. As the step size of the frequency resolution of the controller 540
gets larger, for example, three hundred hertz is a larger step that fifty
hertz, the controller 540 can adjust the driving frequency faster to
match and/or come close to the operational mechanical resonant frequency.
It is further contemplated that a DDS chip can function in a similar
manner with a direct driving system 230 as shown in FIG. 2 and described
previously herein.

[0094]Referring to FIGS. 7A-7D, four flow diagrams are shown that
illustrate the operation of software and/or firmware in or on the
actuator controller 550 and/or the driver assembly 560. According to some
embodiments FIGS. 7A-7D are similar to FIGS. 4A-4D described above. FIG.
7A illustrates an ADC interrupt service method (ISM) 770 according to
some embodiments. As discussed above in relation to FIG. 5, the current
sensor 557 monitors current usage of the driver board 560. The voltage
across the current sensor 557 is proportional to the current drawn across
the resistor R. In step 771, the ADC 541 periodically receives an analog
voltage generated by the current sensor 557 and converts that analog
voltage into a digital voltage value, also known as an ADC digital
voltage value. Once a new digital voltage value is obtained, then in step
772 the oldest stored digital voltage value is subtracted from a running
total by the controller 540 and is stored in random access memory in the
actuator controller 550. Next, in step 773 the oldest subtracted digital
voltage value is then replaced with the new received digital voltage
value and added into the running total by the controller 540. The ADC ISM
770 then awaits its next sample acquisition in step 774, which depends on
a predetermined acquisition time increment.

[0095]Referring to FIG. 7B, a timer interrupt service method (ISM) 776 is
shown according to some embodiments. In step 777, the timer ISM 770
executes to reload the actuator driver. In step 778, the controller 540
converts the running total of digital voltage values (e.g., thirty
digital voltage values) into a running total of digital current values
(778). The running total of digital current values can be averaged by
dividing by the total number of samples (e.g., thirty samples), although
the data can be processed in other manners. This average digital current
value is a first current sample that is about equal to the average
current drawn by the driver board 560 over a predetermined period of time
(e.g., twenty microseconds×thirty samples=600 microseconds).

[0096]After the running total of digital voltage values is converted into
current values in step 778, then in step 779 the controller 540
determines if frequency calibration is enabled. A user or the controller
540 can turn frequency calibration on or off. If in step 779 the
controller 540 determines the frequency calibration is enabled, then the
Yes branch is taken to step 780 where the controller 540 determines if
the driving frequency is being held. If in step 779 the controller 540
determines the frequency calibration is not enabled, then the No branch
is taken to step 781 where the controller 540 reloads a buffer with the
previously stored driving frequency.

[0097]If in step 780 the controller 540 determines the driving frequency
is not being held, then the No branch is taken to step 783 where the
driving frequency will be calibrated by the controller 540 as described
in greater detail below with reference to FIG. 7C. If in step 780 the
controller 540 determines the driving frequency is being held, then the
Yes branch is taken to step 782 where the controller 540 determines if
there is a significant increase in current usage. A significant increase
of current usage can indicate that the actuator device 102 and resonant
driving system 530 is not operating at maximum efficiency and increased
performance because the operational mechanical resonant frequency of the
actuator device 102 has changed.

[0098]If in step 782 the controller 540 determines there is a significant
increase in current usage, then even though there is a hold on the
frequency the Yes branch is taken to step 784 where the controller 540
adjusts the driving frequency and restarts calibration. The default of
the controller 540 is to lower the driving frequency because a
significant increase in current typically indicates a reduction of the
motor system's operational resonant frequency. A significant increase in
current can be at least about five milliamps, but the particular value
can vary between motor types. If in step 782 the controller 540
determines there is not a significant increase in current usage, then the
No branch is taken to step 781 where the controller 540 reloads a buffer
with the previously stored driving frequency.

[0099]Referring back to FIG. 6, as the actuator device 102 warmed up, the
operational mechanical frequency decreased from about 170.8 kilohertz to
about 170 kilohertz. A comparison of the Temp 1 plot to the Temp 2 and
Temp 3 plots illustrate this point. Initially, the minimum current usage
was at fR0, which is at about 170.8 kilohertz. Later on in time, the
minimum current usage was at fR2, which is at about 170.4 kilohertz.
The minimum current usage initially was at about 19 milliamps. If the
driving frequency is maintained at about 170.8 kilohertz, as the
temperature of the actuator device 102 increases, the operational
resonant frequency of the actuator device 102 decreases. If the
operational resonant frequency drops to, for example, 170 kilohertz, FIG.
6 indicates that the current usage will jump to about 20.5 milliamps.
Thus, the default of the timer ISM 776 is to lower the driving frequency
in step 784 after detecting a significant increase of current in step
782. After lowering the driving frequency and restarting calibration in
step 784, the controller 540 loads the buffer with the new driving
frequency in step 781.

[0100]Referring to FIG. 7C, a flow chart is shown that illustrates the
driving frequency calibration method of step 783. Referring also to FIG.
7B, if frequency calibration is enabled in step 779 and the driving
frequency is not held in step 780, then the controller 540 will calibrate
the driving frequency in step 783. Initially, in step 787 the controller
540 determines if an ADC current sample count is less than one. If the
controller 540 determines the ADC current sample count is less than one,
then the Yes Branch is taken to step 781 where the controller 540 reloads
the buffer with the previously stored driving frequency and pulse count
because the controller 540 needs at least two current samples for
comparison. It is contemplated that instead of analyzing and/or comparing
electrical current values to determine change in the operational
mechanical resonant frequency, the controller 540 can analyze and/or
compare other types of values, such as peak-to-peak voltage values, power
values, impedance values, or any combination thereof.

[0101]If the controller 540 determines the ADC current sample count is not
less than one, then the No Branch is taken to step 788 where the
controller determines if the ADC current sample count is equal to one. If
in step 788 the controller 540 determines the ADC current sample count is
equal to one, then the Yes branch is taken to step 789 where a step
direction and a direction change count are cleared and the driving
frequency is stepped down by the controller 540. The change direction
count tracks the number of times the controller 540 changes the step
direction. The step direction determines whether the driving frequency
will be increased or decreased. Clearing the step direction initially
sets the step direction downward in step 789, which incrementally
decreases the driving frequency by the frequency resolution of the
controller 540, although in other embodiments the step direction can be
initially set to upward. Once the driving frequency is lowered in step
789, the controller 540 reloads the buffer with the new driving frequency
in step 781.

[0102]If in step 788 the controller 540 determines the ADC current sample
count is not equal to one that indicates there are at least two ADC
samples available for comparison and the No branch is taken to step 790.
One of the at least two current samples is a minimum recorded current
sample. In step 790, the controller 540 calculates the difference between
the latest current sample with the minimum recorded current sample to
determine if the step direction should change or remain constant.

[0103]In step 791, the controller 540 determines if the latest current
sample has increased. If in step 791 the controller 540 determines the
latest current sample has remained constant or decreased, then the No
branch is taken to step 793 where the driving frequency is stepped by the
frequency resolution of the controller 540 according to the previously
stored step direction (e.g., downward). After the driving frequency is
stepped according to the last direction in step 793, then the controller
540 reloads the buffer with the new driving frequency in step 781. If in
step 791 the controller 540 determines the latest current sample has
increased, then the Yes branch is taken to step 792 where the step
direction is changed and the direction change counter is incremented by
the controller 540. For example, if the initial step direction is
downward, then the direction will be changed to upward.

[0104]In step 794 the controller 540 determines if the direction change
count is greater than two. If in step 794 the controller 540 determines
the direction change count is greater than two, then the Yes branch is
taken to step 795 where the controller 540 resets the driving frequency
to the driving frequency that produced the latest stored minimum current
sample and the resonant driving system 530 is switched to the hold
driving frequency mode. After the driving frequency is reset in step 795,
then the controller 540 reloads the buffer with the new driving frequency
in step 781.

[0105]If in step 794 the controller 540 determines the direction change
count is less than or equal to two, then the No branch is taken to step
796 where the driving frequency is stepped by the frequency resolution of
the controller 540 according to the new step direction (e.g., upward).
After the driving frequency is stepped according to the new step
direction in step 796, then the controller 540 reloads the buffer with
the new driving frequency in step 781.

[0106]Referring to FIG. 7D, a flow diagram of the driver reload method of
step 781 is shown according to some embodiments. Several scenarios in the
timer ISM 776 and the frequency calibration method of step 783 end with
the driver reload method of step 781. In the driver reload method of step
781, the buffer is loaded with the frequency of the driving signal and/or
period if the frequency changed in step 797. After the buffer is
reloaded, the ADC ISM 770 and the timer ISM 776 continue to monitor the
current to determine whether to further adjust the driving frequency of
the driving signals (e.g., driving signals 544a-544b). The controller 540
runs the frequency calibration method of 783 about every eight hundred
microseconds, although the frequency calibration method of step 783 can
be run more or less frequently, for example, every four hundred
microseconds or every sixteen hundred microseconds.

[0107]Now referring to FIG. 8A, a semi-resonant drive actuator system
100(3) in accordance with other embodiments of the present invention is
shown. The semi-resonant drive actuator system 100(3) with an actuator
device 802 which is driven by a driving system 830. As before, the
driving system 830 in this example includes an actuator controller and a
driving system 830. In this example, the actuator controller in driving
system 830 is the same in structure and operation as either actuator
controller system 250 or 550 except as described herein, although other
types of actuator controller systems can be used. By way of example only,
a driving system and method for generating these driving signals for a
full bridge circuit in a driver assembly 260 is described in U.S. patent
application Ser. No. 12/228,943, entitled, "Semi-Resonant Driving Systems
And Methods Thereof", which is herein incorporated by reference in its
entirety.

[0108]Referring more specifically to FIGS. 8A and 8B, the actuator device
802 generates a two-dimensional trajectory to frictionally couple to and
drive a moveable load such as an optical lens by way of example only, in
either of at least two opposing directions, although the actuator device
802 can generate other types of trajectories, be coupled in other manners
and at other locations, and move other types of loads in other
directions. The actuator device 802 includes an asymmetrical, elongated
structure 803, although the actuator device 802 can comprise other types
of structures with other shapes and symmetries. The elongated structure
803 has a depth D with a bending mode having a first nominal mechanical
resonant frequency "fres1" and a height H with a bending mode having a
second nominal mechanical resonant frequency "fres2." The height H is
generally greater than the depth D so the second nominal mechanical
resonant frequency "fres2" is higher than first nominal mechanical
resonant frequency "fres1", although the structure can have other
dimensions. By way of example only, other factors that affect nominal
mechanical resonance frequency include manufacturing tolerances, material
stiffness, mass, and location and orientation of internal electrodes. As
described above, factors that affect an operational mechanical frequency
of the structure 803 include, by way of example only, actuator
temperature and ambient temperature.

[0109]The elongated structure 803 includes four piezoelectric regions 806,
808, 810, and 812, and electrodes 814(1) and 814(2), electrodes 816(1)
and 816(2), electrodes 818(1) and 818(2), and electrodes 820(1) and
820(2), although the structure 803 can comprise other numbers, types and
shapes of structures with other numbers and types of regions and
connectors. By way of example only, in alternative embodiments one of the
two piezoelectric regions 806 and 812 and one of the piezoelectric
regions 808 and 810, could be inactive which would reduce the drive
amplitude, but otherwise would not alter the operation of the actuator
system, although other combinations of active and inactive regions could
be used.

[0110]Each piezoelectric region 806, 808, 810, and 812 has a polarity that
is established by poling during manufacturing, creating a positive
electrode and a negative electrode. The piezoelectric regions 806, 808,
810, and 812 are poled during manufacturing so that "L" shaped electrode
814(1) is negative (A-) and "L" shaped electrode 814(2) is positive (A+)
for region 806, "L" shaped electrode 816(2) is negative (B-) and "L"
shaped electrode 816(1) is positive (B+) for region 812, "L" shaped
electrode 818(1) is negative (C-) and "L" shaped electrode 818(2) is
positive (C+) for region 808, "L" shaped electrode 820(2) is negative
(D-) and "L" shaped electrode 820(1) is positive (D+) for region 810,
although the piezoelectric regions can be formed in other manners. In the
elongated structure 803, the piezoelectric regions 808 and 810 are
located adjacent each other and between outer piezoelectric regions 806
and 812 as illustrated, although the structure could have other numbers
of piezoelectric regions in other configurations.

[0111]The direct driving system 830 is shown operatively coupled to the
actuator device 802. As discussed above, the direct driving system 830
can also be used to drive a variety of different actuator devices
including, but not limited to actuator device 102 and also other linear
motor systems employing multi-layer piezoelectric plates as described in
the aforementioned copending and commonly owned U.S. patent application
Publication Ser. No. 12/228,923; rotary motor systems, semi-resonant
actuator systems as described in the aforementioned copending and
commonly owned U.S. patent Application Publication Ser. No. 12/228,943;
linear tube motor systems, rotary tube motor systems, and ultrasonic
motor systems. The direct driving system 830 can reside on a motherboard
or computer chip. The direct driving system 830 comprises a controller
board or actuator controller system 850 and a driver assembly 860,
although other numbers and types of boards or chips can be used. The
driver assembly 860 can also be referred to as an actuator driver or a
motor driver.

[0112]The actuator controller system 850 includes a processing system or
controller 840, a supply voltage or voltage source 853, a current sensor
857, and a filter 859, although the actuator controller system 850 can
include other types and numbers of systems, devices, and components which
are connected in other manners. The controller 840 can be a processor, a
microprocessor, a microcontroller, a digital signal processor or other
controller motherboard, although other numbers and types of controllers
can be used. The voltage source 853 is a battery that supplies power to
run, for example, the actuator device 802 and the various onboard
electronics (e.g., controller 840), although other types and numbers of
power supplies can be used. In this example, the voltage source 853 can
supply a voltage of approximately 1.5 volts to approximately 3.3 volts,
although other ranges of voltages could be supplied and used. The voltage
source 853 is coupled to the driver assembly 860.

[0113]The current sensor 857 is coupled between the voltage source 853 and
the driver assembly 860 and monitors current usage of the driver assembly
860. The current sensor 857 detects an analog voltage drop across
resistor R which is proportional to the current drawn across the resistor
R by the driver assembly 860 for a fixed operating speed of the actuator
device 802 and the direct driving system 830. Thus, the voltage drop can
be used to calculate the current drawn by the actuator device 802 and the
direct driving system 830 using a multiplier.

[0114]The resistor R can have a resistance from about 0.025 ohms to about
1 ohms, although other ranges for the resistance and other types and
numbers of resistors in other combinations can be used, depending upon
the expected current usage. As the resistance of resistor R increases,
the voltage drop across the resistor R increases, which increases the
sensitivity of the current sensor 857. However, a larger voltage drop may
require a more powerful voltage source to maintain a sufficient power
supply to run the direct drive actuator system 100(3) and the onboard
electronics. The current sensor 857 also is coupled to the filter 889,
which removes the AC drive frequency component, although other
configurations can be used, such as having the current sensor 857
directly coupled to the controller 840 without a filter.

[0115]The controller 840 is directly coupled to the voltage source 853 and
to the filter 859, although the controller 840 could have other types and
numbers of connections. The controller 840 includes an analog-to-digital
converter 841 ("ADC") and a pulse width modulated ("PWM") signal
generator 842, although the controller 840 can include other types and
numbers of systems, devices, assemblies, and components in other
configurations, such as a master clock described later herein. The
analog-to-digital converter 841 receives the analog voltage signal as an
input from the filter 859 and converts that analog voltage signal into a
digital voltage value. The pulse width modulated signal generator 842 is
coupled to the driver assembly 860. The pulse width modulated signal
generator 842 generates low-voltage driving signals 842(1) and 844(1),
although the pulse width modulated signal generator 842 could generate
other numbers and types of signals. Inverters 845(1) and 845(2) are
coupled to the pulse width modulated signal generator 842 and receive the
low-voltage driving signals 842(1) and 844(1) which are inverted to
generate additional low-voltage driving signals 842(2) and 844(2),
respectively. The low voltage and inverted driving signals 842(1),
842(2), 844(1), and 844(2) are coupled through the driver assembly 860 on
to outputs 824(1)-824(4) to drive the four piezoelectric regions 806,
808, 810, and 812, although other numbers and types of signals could be
generated and used.

[0116]In this example, the controller 840 uses a multiplier, the value of
which is based on sensor resistor R and type of current sensor
electronics 857, to convert the digital voltage value into a digital
current value, which is used to determine a driving frequency of the
low-voltage driving signals 842(1), 842(2), 844(1), and 844(2). The
controller 840 can use the digital current value, a plurality of digital
current values, or an average digital current value to determine if an
adjustment to the drive frequency is getting closer or farther from the
operational mechanical resonant frequency of the actuator device 802. Put
another way, the controller 840 can cause the PWM signal generator 842 to
adjust a driving frequency of a generated signal (e.g., low-voltage
driving signals 842(1), 842(2), 844(1), and 844(2) up or down based at
least in part on digital current values.

[0117]The driver assembly 860 includes a pair of full bridge drive
circuits 822(1) and 822(2) each of which are coupled to the voltage
source 853 and have four outputs 824(1)-824(4) which provide ultrasonic,
square wave driving signals 842(1), 842(2), 844(1), and 844(2), although
other types and numbers of driving circuits and systems, such as a half
bridge circuit system by way of example only, with other number of
outputs which provide other types of signals, such as sinusoidal
shaped-signals by way of example only, can be used. The output 824(1)
from full bridge drive circuit 822(1) is coupled to electrodes 814(1) and
816(1), the output 824(2) from full bridge drive circuit 822(1) is
coupled to electrodes 814(2) and 816(2), the output 824(3) from full
bridge drive circuit 822(2) is coupled to electrodes 818(1) and 820(1),
and the output 824(4) from full bridge drive circuit 822(2) is coupled to
electrodes 818(2) and 820(2), although other types and numbers of
connections could be used

[0118]Although a full bridge drive circuit has been described, other types
of driving systems can be used. One of the advantages of using a full
bridge drive circuit is that the effective voltage differential across
the positive electrode and negative electrode of each of the
piezoelectric members (e.g., piezoelectric members 132a-132d) is twice
the supply voltage, which effectively doubles the mechanical output as
compared with a half bridge circuit with the same supply voltage, which
saves space. U.S. patent application Ser. No. 12/228,923, entitled,
"Reduced-Voltage, Linear Motor Systems and Methods Thereof" provides
additional description of the full bridge drive circuit along with the
driving signals which are generated which is herein incorporated by
reference in its entirety. Since the components and operation of half
bridge drive circuits and full bridge drive circuits are well known to
those of ordinary skill in the art, they will not be described in greater
detail herein.

[0119]The operation of the semi-resonant actuator system 800 will now be
described with reference to FIGS. 8A and 8B. As described above, the
elongated structure 803 has two bending modes, mode1 and mode2, which
each having different nominal and operational mechanical resonant
frequencies. The vibration amplitude in either of these bending modes is
dependent on the driving frequency of the applied driving signals. When
the driving system 830 applies driving signals at the nominal and/or
operational mechanical resonant frequency for one of the bending modes,
such as the frequency "fres1" of mode1 to both bending modes of the
structure 803, the vibration amplitude is fully amplified for the bending
mode operating at its operational mechanical resonant frequency and is
only partially amplified for the other bending mode which is operating at
partial resonance. When the driving system 830 applies driving signals at
the operational mechanical resonant frequency "fres2" for the other one
of the bending modes, such as the frequency of mode2, to both bending
modes of the structure 803, the vibration amplitude is fully amplified
for the bending mode operating at its operational mechanical resonant
frequency and is only partially amplified for the other bending mode
which is operating at partial resonance.

[0120]Partial resonance can also be referred to as semi-resonance, which
is now described in greater detail. In a typical mechanical system under
forced excitation at frequency f, the normalized amplitude A is:

A = Q M z 2 + ( z 2 - 1 ) 2 Q M 2 ##EQU00001##

[0121]where A is the amplitude (relative to DC level Ao).

z = f f o ##EQU00002##

[0122]where fo is the nominal mechanical resonant frequency of this
system and f is the driving frequency. QM is the mechanical quality
factor, (QM can be as high as 100 or more). For a typical amplitude
resonance curve for frequency from 0 (DC) to well past nominal mechanical
resonant frequency (fo), amplitude A at DC is normalized to 1;
amplitude A at resonance (f=fo) is amplified by QM; amplitude
at f>>fo drops to close to 0. Amplitude A can range from 1 (at
DC) to QM at resonant frequency. In these embodiments, partial
resonance or semi-resonance occurs when A ranges between about 2 to

Q M 2 , ##EQU00003##

although other ranges outside of this range could be used, such as when A
is between 1 and QM could be used.

[0123]Four driving signals 842(1), 842(2), 844(1), and 844(2) are
transmitted from the outputs 824(1)-824(4) of the full bridge drive
circuits 822(1) and 822(2) to respective electrodes on the structure 803.
The driving signals from outputs 824(1)-824(2) are phase shifted by the
driving system 830 with respect to the driving signals from outputs
824(3)-824(4) between about zero degrees to about ninety degrees for
moving the movable member in one of the two directions, although other
ranges for the phase shift can be used. Additionally, the driving system
830 adjusts the phase shift to between about negative one hundred eighty
degrees to about negative ninety degrees for moving the movable member in
the opposite direction between outputs 824(1)-824(2) and outputs
824(3)-824(4), although other ranges for the phase shift can be used.

[0124]The driving system 830 includes a controller 840 that monitors
and/or analyzes at least one of current values, voltage values, power
values, impedance values, or any combination. The controller 840 in
driving system 830 monitors current usage of the semi-resonant actuator
system 100(3) and compares a first current value with a second current
value to determine changes in the operational mechanical resonant
frequency of one of the two bending modes of the actuator device 802. In
these embodiments, the controller 840 in the driving system 830 monitors
and adjusts and/or steps the driving frequency of the driving signals to
keep the driving frequency close to or at a fixed offset from the
operational mechanical resonant frequency of the bending mode operating
at full resonance. The controller 840 in the driving system 830 does not
adjust the driving frequency based on the operational mechanical resonant
frequency of the bending mode operating at partial resonance.

[0125]In embodiments of the present invention, it is contemplated that in
the operation of an actuator device 102 and 802, only one of the two
bending modes is controlled by the direct driving system 230, discussed
above and shown in FIG. 2, or by the resonant driving system 530,
discussed above and shown in FIG. 5, or by the driving system 830. In one
embodiment, the driving signals from outputs 824(3)-824(4) are provided
to resonant piezoelectric regions 808 and 810 at a frequency close to or
at a fixed offset from the operational mechanical resonant frequency of
the bending mode of the actuator device 802 in the X-Z plane, with the
driving signals from outputs 824(1)-824(2) provided to the piezoelectric
regions 806 and 812 at the same frequency. Further details on the
structure and operation of the actuator device 802 along with the driving
system 830 may be found in the aforementioned copending and commonly
owned U.S. patent application Publication Ser. No. 12/228,943, with
reference in particular to FIGS. 1-11B, and the written description
thereof which again is incorporated by reference in its entirety herein.

[0126]Although embodiments of examples of the driving systems 230, 530,
and 830 including processing systems or controllers 240, 540, and 840,
respectively, are described and illustrated herein, the driving systems
230, 530, and 830 including processing systems or controllers 240, 540,
and 840, respectively, each can be implemented on any suitable computer
system or computing device. It is to be understood that the devices and
systems of the embodiments described herein are for exemplary purposes,
as many variations of the specific hardware and software used to
implement the embodiments are possible, as will be appreciated by those
skilled in the relevant art(s).

[0127]Furthermore, each of the systems of the embodiments may be
conveniently implemented using one or more general purpose computer
systems, microprocessors, digital signal processors, and
micro-controllers, programmed according to the teachings of the
embodiments, as described and illustrated herein, and as will be
appreciated by those ordinary skill in the art.

[0128]In addition, two or more computing systems or devices can be
substituted for any one of the systems in any embodiment of the
embodiments. Accordingly, principles and advantages of distributed
processing, such as redundancy and replication also can be implemented,
as desired, to increase the robustness and performance of the devices and
systems of the embodiments. The embodiments may also be implemented on
computer system or systems that extend across any suitable network using
any suitable interface mechanisms and communications technologies,
including by way of example only telecommunications in any suitable form
(e.g., voice and modem), wireless communications media, wireless
communications networks, cellular communications networks, G3
communications networks, Public Switched Telephone Network (PSTNs),
Packet Data Networks (PDNs), the Internet, intranets, and combinations
thereof.

[0129]The embodiments may also be embodied as a computer readable medium
having instructions stored thereon for one or more aspects of the present
invention as described and illustrated by way of the embodiments herein,
as described herein, which when executed by a processor, cause the
processor to carry out the steps necessary to implement the methods of
the embodiments, as described and illustrated herein.

[0130]A variety of applications exist for the exemplary actuator systems,
such as the direct drive actuator system 100(1), the resonant drive
actuator system 100(2), and the semi-resonant drive actuator system
100(3), described and illustrated herein. For example, several
alternative applications for such actuator systems can be found in U.S.
Pat. No. 6,940,209, titled, "Ultrasonic Lead Screw Motor"; U.S. Pat. No.
7,339,306, titled, "Mechanism Comprised of Ultrasonic Lead Screw Motor";
U.S. Pat. No. 7,170,214, titled, "Mechanism Comprised of Ultrasonic Lead
Screw Motor"; and U.S. Pat. No. 7,309,943, titled, "Mechanism Comprised
of Ultrasonic Lead Screw Motor," all of which are commonly assigned to
New Scale Technologies, Inc.

[0131]Having thus described the basic concept of the invention, it will be
rather apparent to those skilled in the art that the foregoing detailed
disclosure is intended to be presented by way of example only, and is not
limiting. Various alterations, improvements, and modifications will occur
and are intended to those skilled in the art, though not expressly stated
herein. These alterations, improvements, and modifications are intended
to be suggested hereby, and are within the spirit and scope of the
invention. Additionally, the recited order of processing elements or
sequences, or the use of numbers, letters, or other designations
therefore, is not intended to limit the claimed processes to any order
except as may be specified in the claims. Accordingly, the invention is
limited only by the following claims and equivalents thereto.